The present invention relates to a variable valve operating system of an internal combustion engine enabling valve-lift characteristic (valve lift and event) to be varied, and in particular being capable of continuously simultaneously changing all of valve lift and working angle of an intake valve depending on engine operating conditions.
There have been proposed and developed various internal combustion engines equipped with a variable valve operating system enabling valve-lift characteristic (valve lift and working angle) to be continuously varied depending on engine operating conditions, in order to reconcile both improved fuel economy and enhanced engine performance through all engine operating conditions. One such variable valve operating system has been disclosed in Japanese Patent Provisional Publication No. 8-260923 (corresponding to U.S. Pat. No. 5,636,603 issued Jun. 10, 1997 to Makoto Nakamura et al.). The variable valve operating system disclosed in U.S. Pat. No. 5,636,603 is comprised of a variable working angle control mechanism capable of variably continuously controlling a working angle of an intake valve depending on engine operating conditions. The variable valve operating system disclosed in U.S. Pat. No. 5,636,603 is comprised of a drive shaft, a control shaft, an annular disc (or an intermediate member), and a cam. The drive shaft is rotatably supported on an engine body in such a manner as to rotate in synchronism with rotation of the engine crankshaft. The control shaft is also rotatably supported on the engine body so that an angular position of the control shaft is variably controlled by means of a hydraulic actuator. The annular disc is mechanically linked to the drive shaft, so that rotary motion of the drive shaft is transmitted via a pin to the annular disc. The central position of rotary motion of the annular disc displaces or shifts relative to the engine body depending on a change in the angular position of the control shaft. The cam rotates in synchronism with rotary motion of the annular disc to open and close an intake valve. Changing the center of rotary motion of the annular disc causes ununiform rotary motion of the annular disc itself, consequently ununiform rotary motion of the cam, and thus an intake valve open timing (IVO), an intake valve closure timing (IVC), and a working angle (a lifted period) of the intake valve vary. The system disclosed in U.S. Pat. No. 5,636,603 has a control-shaft position sensor or a control-shaft rotation angle sensor that detects an actual angular position of the control shaft and generates a sensor signal indicative of the actual angular position of the control shaft. A potentiometer is used as such a position sensor. The previously-noted hydraulic actuator is closed-loop controlled based on the sensor signal output from the position sensor, so that the actual angular position of the control shaft is brought closer to a desired angular position based on the engine operating conditions.
In the variable valve operating system of U.S. Pat. No. 5,636,603, the control-shaft position sensor (potentiometer) is attached onto or directly coupled with the control shaft end. Directly coupling the control-shaft position sensor to the control shaft end, permits vibrations and loads input into the control shaft to be transferred therefrom directly into the control-shaft position sensor. This reduces the durability of the control-shaft position sensor. Actually, the control shaft receives various loads due to a valve-spring reaction force and inertia forces of moving parts. During input-load application to the control shaft, a change in relative position between the axis of the control shaft and the axis of the control-shaft position sensor occurs owing to a radial displacement of the control shaft within a clearance of a control-shaft bearing whose outer race is fitted to the engine body. As appreciated, the relative-position change exerts a bad influence on the durability of the control-shaft position sensor. To avoid this, the control shaft end and the control-shaft position sensor may be coupled with each other by means of a coupling mechanism that permits a change in relative position between the control shaft end and the control-shaft position sensor. In lieu thereof, a non-contact position sensor such as an electromagnetic rotation angle sensor, may be used to detect the actual angular position of the control shaft. However, suppose that the coupling mechanism is merely disposed between the control shaft end and the control-shaft position sensor without deliberation or the non-contact position sensor is used in a manner so as to permit the relative-position change. There is a problem of a great error contained in the position sensor signal output owing to such a relative-position change. The great error reduces the detection accuracy of the control-shaft position sensor. Therefore, it is desirable to effectively suppress the detection accuracy of the control-shaft position sensor from being reduced due to a change in relative position between the control shaft end and the control-shaft position sensor, which may occur owing to input load applied to the control shaft, while permitting the relative-position change.
Accordingly, it is an object of the invention to provide a variable valve operating system of an internal combustion engine enabling valve-lift characteristic to be continuously varied, which avoids the aforementioned disadvantages.
In order to accomplish the aforementioned and other objects of the present invention, a variable valve operating system of an internal combustion engine comprises a drive shaft adapted to be rotatably supported on an engine body and to rotate about an axis in synchronism with rotation of a crankshaft of the engine, a control shaft adapted to be rotatably supported on the engine body, an actuator driving the control shaft to adjust an angular position of the control shaft, an intermediate member that rotary motion of the drive shaft is converted into either of rotary motion and oscillating motion of the intermediate member, a center of the motion of the intermediate member with respect to the engine body varying depending on the angular position of the control shaft, the intermediate member linked to an intake valve of the engine, for lifting the intake valve responsively to the motion of the intermediate member, a valve lift characteristic of the intake valve being varied depending on a change in the center of the motion of the intermediate member, a position sensor attached to the engine body to generate a sensor signal indicative of the angular position of the control shaft, the position sensor having a directivity for an error contained in the sensor signal owing to a change in relative position between a center of the control shaft and the position sensor, the error becoming a minimum value in a specified direction of the relative position change, and the specified direction of the relative position change being set to be substantially identical to a direction of a line of action of load acting on the center of the control shaft during idling.
According to another aspect of the invention, a variable valve operating system of an internal combustion engine comprises a drive shaft adapted to be rotatably supported on an engine body and to rotate about an axis in synchronism with rotation of a crankshaft of the engine, the drive shaft having a first eccentric cam fixedly connected to an outer periphery of the drive shaft, a link arm rotatably fitted onto an outer periphery of the first eccentric cam, a control shaft adapted to be rotatably supported on the engine body, the control shaft formed integral with a second eccentric cam, an actuator driving the control shaft to adjust an angular position of the control shaft, a rocker arm rotatably supported on an outer periphery of the second eccentric cam so that the oscillating motion of the rocker arm is created by the link arm, a rockable cam rotatably fitted on the outer periphery of the drive shaft, a link member mechanically linking the rocker arm to the rockable cam so that the oscillating motion of the rocker arm is converted into an oscillating motion of the rockable cam and that the intake valve is pushed by the oscillating motion of the rockable cam, a valve lift and a working angle of the intake valve simultaneously varying by changing an angular position of the second eccentric cam of the control shaft, a position sensor attached to the engine body to generate a sensor signal indicative of the angular position of the control shaft, the position sensor having a directivity for an error contained in the sensor signal owing to a change in relative position between a center of the control shaft and the position sensor, the error becoming a minimum value in a specified direction of the relative position change, and the specified direction of the relative position change being set to be substantially identical to a direction of a line segment interconnecting a center of the drive shaft and the center of the control shaft, during idling.
According to a further aspect of the invention, an internal combustion engine comprises a variable lift and working angle control mechanism that enables both a valve lift and a working angle of an intake valve to be continuously simultaneously varied depending on engine operating conditions, the variable lift and working angle control mechanism comprising a drive shaft adapted to be rotatably supported on an engine body and to rotate about an axis in synchronism with rotation of a crankshaft of the engine, a control shaft adapted to be rotatably supported on the engine body, an actuator driving the control shaft to adjust an angular position of the control shaft, and an intermediate member through which rotary motion of the drive shaft is converted into either of rotary motion and oscillating motion of the intermediate member, a center of the motion of the intermediate member with respect to the engine body varying depending on the angular position of the control shaft, the intermediate member linked to the intake valve, for lifting the intake valve responsively to the motion of the intermediate member, and a valve lift characteristic including both the valve lift and the working angle of the intake valve being varied depending on a change in the center of the motion of the intermediate member, sensor means attached to the engine body for generating a sensor signal indicative of the angular position of the control shaft, the sensor means having a directivity for an error contained in the sensor signal owing to a change in relative position between a center of the control shaft and the sensor means, the error becoming a minimum value in a specified direction of the relative position change, and the specified direction of the relative position change being set to be substantially identical to a direction of a line of action of load acting on the center of the control shaft during idling.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.